Systems and methods for use with an implantable medical device for discriminating vt and svt based on ventricular depolarization event timing

ABSTRACT

Techniques are described for discriminating ventricular tachycardia (VT) from supraventricular tachycardia (SVT) using an implantable medical device capable of multi-site ventricular sensing. In one example, ventricular depolarization events are detected within a patient by the implantable device during a tachyarrhythmia, at both a left ventricular sensing site and a right ventricular sensing site. Ventricular event timing differences are then ascertained. The device compares the ventricular event timing differences detected during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient, such as event timing differences previously detected within the patient during sinus rhythm or extrapolated from sinus rhythm values. The device then distinguishes VT from SVT based on the comparison of the event timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences. Morphological waveform analysis can also be performed, when needed, to further distinguish VT from SVT.

FIELD OF THE INVENTION

The invention generally relates to implantable cardiac stimulationdevices, such as pacemakers, implantable cardioverter/defibrillators(ICDs) or cardiac resynchronization therapy defibrillators (CRT-Ds) and,in particular, to techniques for discriminating ventricular tachycardia(VT) from supraventricular tachycardia (SVT) using such devices.

BACKGROUND OF THE INVENTION

A pacemaker is a medical device for implant within a patient thatrecognizes various arrhythmias such as tachycardia and delivers pacingtherapy to the heart in an effort to remedy the arrhythmia. An ICD is adevice, also for implant within a patient, which additionally recognizesatrial fibrillation (AF) or ventricular fibrillation (VF) and deliverselectrical shocks to terminate the fibrillation. Within pacemakers andICDs, it is important to distinguish a tachycardia that arises in theventricles from those that arise elsewhere in the heart. A tachycardiathat arises in the ventricles (referred to as VT) is often more seriousthan a tachycardia arising elsewhere in the heart, since VT cansometimes lead to VF, which is fatal if untreated. Moreover, the type oftherapy to be delivered to the heart of the patient depends upon thesource of the tachycardia. In particular, it is important todiscriminate SVT from VT. SVT is a tachyarrhythmia whose origin is abovethe ventricles but which is conducted into the ventricles, resulting inunacceptably rapid ventricular rate. The true underlying arrhythmia inthese cases may be AF, sinus tachycardia (ST), ectopic atrialtachycardia, atrial reentry tachycardia, atrioventricular (NV) nodalreentry tachycardia, paroxysmal AF or atrial flutter.

Failure to distinguish SVT from VT can result in delivery ofinappropriate therapy. Depending upon the capabilities of the implanteddevice, inappropriate therapy might include delivery of unnecessaryanti-tachycardia pacing (ATP) to the ventricles in response to an SVT(that has been misidentified as VT) or delivery of unneededcardioversion shocks to the atria in response to a VT (that has beenmisidentified as SVT.) Misidentification of SVT and VT is one of theleading causes of improper device therapy, inclining the delivery ofpainful and unnecessary cardioversion shocks.

Accordingly, it would be highly desirable to efficiently and reliablydistinguish SVT from VT. Waveform morphology comparison may be employedin an attempt to achieve such discrimination. Waveform discriminationtechniques are described in, e.g., U.S. Pat. No. 5,273,049 to Steinhaus,et al. entitled, “Detection of Cardiac Arrhythmias using TemplateMatching by Signature Analysis”; U.S. Pat. No. 5,240,009 to Williams,entitled “Medical Device with Morphology Discrimination”; U.S. Pat. No.5,779,645 to Olson, et al., “System and Method for Waveform MorphologyComparison”; and U.S. Pat. No. 6,516,219 to Street, entitled “ArrhythmiaForecasting based on Morphology Changes in Intracardiac Electrograms.”See, also, the improved morphology-based discrimination techniquesdescribed in U.S. patent application Ser. No. 11/674,974, filed Feb. 14,2007, of Graumann, entitled “System and Method for Morphology-BasedArrhythmia Discrimination using Left Ventricular Signals sensed by anImplantable Medical Device.”

Other techniques for distinguishing VT and SVT include “sudden onsetdiscrimination” and “PR logic discrimination.” Sudden onsetdiscrimination is discussed, e.g., in U.S. Pat. No. 6,636,764 to Fain,et al., entitled “Safety Backup in Arrhythmia Discrimination Algorithm.”PR logic discrimination is discussed, e.g., in U.S. Pat. No. 7,058,450to Struble, et al., entitled “Organizing Data according to CardiacRhythm Type.”

However, waveform discrimination, sudden onset discrimination and PRlogic discrimination may not be optimal or sufficient in distinguishingVT from SVT, and inappropriate cardioversion shocks continue to be aproblem. Also, accurate waveform discrimination can be computationallyintensive, thereby consuming device resources.

Accordingly, it would be desirable to provide improved techniques fordistinguishing VT and SVT and aspects of the invention are directed tothat end.

SUMMARY OF THE INVENTION

In accordance with exemplary implementations of the invention, a methodis provided for use by an implantable medical device capable ofmulti-site ventricular sensing within a patient. Intrinsic ventricularelectrical events are detected by the device within the patient during atachyarrhythmia at each of a plurality of different sites within theventricles. Ventricular event timing differences are then detectedbetween the ventricular events (as detected at the plurality ofdifferent sites.) The device compares the ventricular event timingdifferences during the tachyarrhythmia with predeterminedsupraventricular event timing differences for the patient, such as eventtiming differences previously detected within the patient during sinusrhythm or extrapolated from sinus rhythm values. The device thendistinguishes VT from SVT based on the comparison of ventricular eventtiming differences detected during the tachyarrhythmia with thepredetermined supraventricular event timing differences, at least incases where the comparison is sufficient to allow such a determinationto be made. In circumstances where the timing difference comparison isnot sufficient to discriminate VT from SVT (such as if magnitude of anytiming differences is below a noise level), morphological analysis canbe additionally performed to distinguish VT from SVT. In this manner,timing differences between events sensed at different sites within theventricles are employed—either alone in or combination with eventmorphology—to discriminate VT and SVT.

By exploiting ventricular event timing differences, VT can often beefficiently and reliably distinguished from SVT without the need toperform a more computationally intensive morphology comparison.Nevertheless, in circumstances where morphology comparison is needed,the device is equipped to perform such a comparison.

In various exemplary embodiments described herein, the implantablemedical device is a pacer/ICD or a CRT-D equipped with separate RV andLV leads, each with tip and ring electrodes for bipolar sensing. Duringa tachyarrhythmia characterized by a high ventricular rate, the deviceseparately detects ventricular depolarization events in the RV (i.e. RVQRS complexes) and in the LV (i.e. LV QRS complexes) and compares therelative timing of the events to detect timing differences between theRV and LV events (herein denoted T_(RV-LV).) Preferably, the timingdifferences are averaged over several ventricular beats to provide anaverage value for T_(RV-LV). For a given patient, T_(RV-LV) might bepositive, negative or zero. The average value for T_(RV-LV) is comparedagainst a predetermined supraventricular RV-LV timing difference (hereindenoted T_(RV-LV/SV)), which may have been obtained in advance withinthe patient during normal sinus rhythm or extrapolated from sinus rhythmvalues to take changes in ventricular rate into account. The subscript“SV” is used to indicate that this timing delay is representative of asupraventricular rhythm, which can include sinus rhythm.

In a first illustrative embodiment, T_(RV-LV/SV) is predetermined basedon sinus rhythm timing delays, without taking into account possiblevariations in the timing delays due to increasing ventricular rate. Thatis, T_(RV-LV/SV) represents the average intrinsic RV-LV timing delayduring normal sinus rhythm within the patient. For a given patient,T_(RV-LV/SV) might be positive, negative or zero. The particularT_(RV-LV/SV) value for the patient may be ascertained, for example, byan external programmer during a follow-up session with a clinicianfollowing implant of the device into the patient wherein sinus rhythmvalues are averaged. If so, the average value is then programmed intothe implantable device. In other examples, the implantable device itselfdetects or updates the values for T_(RV-LV/SV) based on cardiac signalssensed within the patient during sinus rhythm. In any case, during atachyarrhythmia, the average value T_(RV-LV/SV) is retrieved by theimplantable device from memory for comparison against the current valueof T_(RV-LV). The magnitude of the difference between T_(RV-LV) andT_(RV-LV/SV) is calculated using T_(DIFF)=|T_(RV-LV)−T_(RV-LV/SV)|. IfT_(DIFF) is relatively large (as determined using a suitable thresholdT_(DIFF) _(—) _(MAX)), then the implantable medical device promptlyidentifies the ongoing tachyarrhythmia as VT without the need for anyfurther analysis. In one particular example, T_(DIFF) _(—) _(MAX) is setto two times the standard deviation of the sinus rhythm RV-LV timingdelay

In this regard, if T_(DIFF) is relatively large, that indicates that thedifference between tachyarrhythmia event timing delays and thepreviously-detected sinus rhythm event timing delays is likewiserelatively large. Any significant difference between tachyarrhythmiatiming and sinus rhythm timing indicates that the tachyarrhythmia has adifferent origin from that of sinus rhythm. Since sinus rhythm is knownto be of supraventricular origin, the origin of the tachyarrhythmia isthereby deemed to be non-supraventricular in origin and so thetachyarrhythmia is identified as VT. For further specificity, the devicecan also examine the signs of T_(RV-LV) and T_(RV-LV/SV). If the signsof T_(RV-LV) and T_(RV-LV/SV) are found to differ from one another (e.g.T_(RV-LV) is positive but T_(RV-LV/SV) is negative), then the signreversal further confirms that the origin of the tachyarrhythmia isventricular in origin. Note that, in this first illustrative embodiment,if T_(DIFF) is not found to be greater than T_(DIFF) _(—) _(MAX), thenthe origin of the tachyarrhythmia is deemed to be inconclusive, sinceT_(DIFF) is not large enough to warrant a determination of a ventricularorigin.

In a second illustrative embodiment, the implantable medical deviceconsiders the current ventricular rate in determining T_(DIFF). Morespecifically, values of T_(RV-LV/SV) are obtained in advance for thepatient over a range of sinus rhythm heart rates, including relativelyhigh sinus rhythm rates. The T_(RV-LV/SV) values may be stored in ahistogram as a function of rate. Based on the sinus rhythm values storedin the histogram, the implantable device then extrapolates into theVT/SVT zone to estimate values for T_(RV-LV/SV) values at the highventricular rates associated with VT/SVT. These values are referred toherein as T_(RV-LV/SV)(rate) values. Alternatively, theT_(RV-LV/SV)(rate) values may be ascertained by an external programmerduring a follow-up session, then programmed into the implantable device.In any case, upon detection of a tachyarrhythmia within the patient, theimplantable device retrieves the particular value of T_(RV-LV/SV)(rate)appropriate to the current ventricular rate. The average value forT_(RV-LV) obtained during the tachyarrhythmia is then compared againstT_(RV-LV/SV)(rate). The magnitude of the difference between T_(RV-LV)and T_(RV-LV/SV)(rate) is calculated usingT_(DIFF)(rate)=|T_(RV-LV)−T_(RV-LV/SV)(rate)|.

If T_(DIFF)(rate) is relatively large (i.e. T_(DIFF)(rate)>T_(DIFF) _(—)_(MAX)(rate) where T_(DIFF) _(—) _(MAX)(rate) is a predeterminedrate-dependent threshold), then the device promptly identifies theongoing tachyarrhythmia as VT. For further specificity, the device canexamine the signs of T_(RV-LV) and T_(RV-LV/SV)(rate). If the signs arefound to differ from one another, then the sign reversal furtherconfirms that the origin of the tachyarrhythmia is ventricular. Notethat, if T_(DIFF)(rate) is not found to be greater than T_(DIFF) _(—)_(MAX)(rate), then the origin of the tachyarrhythmia is deemedinconclusive.

In a third illustrative embodiment, the implantable medical device alsotakes QRS waveform morphology into account to provide furtherspecificity, particularly in circumstances where the event timinganalysis is inconclusive. In this regard, templates representative ofSVT morphology (QRS_(MORPH/SVT)) and VT morphology (QRS_(MORPH/SVT)) areobtained in advance for the patient. The templates may be derived, forexample, based on intracardiac electrogram (IEGM) traces obtained withinthe patient during previous episodes of SVT or VT. Upon detection of atachyarrhythmia within the patient characterized by a high ventricularrate, the device retrieves the morphology templates as well as theappropriate value of T_(RV-LV/SV)(rate) for current ventricular rate.The average value for T_(RV-LV) is again calculated and compared againstT_(RV-LV/SV)(rate) to determine a value for T_(DIFF)(rate).

As in the preceding embodiment, if T_(DIFF)(rate) is relatively large(i.e. T_(DIFF)(rate)>T_(DIFF) _(—) _(MAX)(rate)), then the deviceidentifies the ongoing tachyarrhythmia as VT based solely on the timingdifference. However, if T_(DIFF)(rate) is not large (i.e. T_(DIFF)(rate)T_(DIFF) _(—) _(MAX)(rate)), then the device compares the waveformsobtained during the tachyarrhythmia (QRS_(MORPH)) with QRS_(MORPH/SVT)and/or QRS_(MORPH/SVT) to distinguish between VT and SVT. If theQRS_(MORPH) is consistent with QRS_(MORPH/SVT) but not QRS_(MORPH/VT),then the tachyarrhythmia is identified as SVT. If the QRS_(MORPH) isconsistent with QRS_(MORPH/SVT) but not QRS_(MORPH/SVT), then thetachyarrhythmia is identified as VT.

For additional specificity, the device can also examine the signs ofT_(RV-LV) and T_(RV-LV/SV)(rate), as already discussed. Still further,the device can examine signals received from additional sensing sitessuch as signals sensed via LV or RV shocking coils. Sensing leads placedon or near the His bundle are also particularly useful fordifferentiating VT and SVT. Sensing sites in the atria can also beuseful. Event timing and/or QRS morphology analysis can be applied tothe additional signals to further confirm the discrimination of VT fromSVT. The use of additional sensing sites may be particularly useful incircumstances where T_(DIFF)(rate)≦T_(DIFF) _(—) _(MAX)(rate) to providefurther specificity.

In any of the various embodiments, once the type of tachyarrhythmia isdetermined, suitable therapy is delivered, such as Atrial ATP inresponse to SVT or cardioversion therapy in response to VT, ifwarranted. Appropriate diagnostic data can be stored within the devicefor subsequent clinician review. In some cases, warning signals can begenerated to alert the patient to seek medical attention.

Thus, in the various exemplary embodiments just summarized, multiplesensing sites are used to monitor the timing of intrinsic heart events.Events with different origination typically present a different timesequence landmark/trace at different sensing sites, which theimplantable system exploits using the aforementioned techniques todetermine/discriminate the origin of the events and thereby discriminateVT from SVT. In addition to VT/SVT discrimination, the method can beused to detect premature ventricular contractions (PVCs) that originatein the ventricles. Although bipolar sensing examples have been describedwherein “near field” signals are sensed in the ventricles using bipolarleads, “far field” sensing may also provide useful information. Also, itshould be understood that the techniques described herein do not requireboth RV and LV sensing leads. In other examples, an RV lead is exploitedthat permits sensing at multiple sites in the RV, such as by using an RVtip/ring electrode pair to sense at one site and an RV coil to sense atanother.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further features, advantages and benefits of the inventionwill be apparent upon consideration of the present description taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates pertinent components of an implantable medical systemhaving a pacemaker, ICD or CRT-D equipped to implement eventtiming-based VT/SVT discrimination, supplemented by waveform morphologydiscrimination, where appropriate;

FIG. 2 is a flow chart providing an overview of the event timing-basedVT/SVT discrimination techniques used by the system of FIG. 1;

FIG. 3 is a simplified illustration of the device of FIG. 1 along with aset of exemplary leads implanted in the heart of the patient,particularly showing, in stylized form, the conduction of electricalsignals to the ventricles from the sinus node during sinus rhythm;

FIG. 4 is another illustration of the device of FIG. 1 particularlyshowing the conduction of electrical signals within the ventriclesduring a VT that originates in the RV;

FIG. 5 is another illustration of the device of FIG. 1, particularlyshowing the conduction of electrical signals within the ventriclesduring a VT that originates in the LV;

FIG. 6 is a flowchart illustrating a first exemplary discriminationtechnique in accordance with the general technique of FIG. 2, whichexploits event timing differences between the LV and RV;

FIG. 7 is a flowchart illustrating a second exemplary discriminationtechnique similar to that of FIG. 6, but which additionally exploits theventricular rate in assessing event timing differences;

FIG. 8 is a flowchart illustrating a third exemplary discriminationtechnique similar to that of FIG. 7, but which additionally exploitsmorphology templates to provide further specificity;

FIG. 9 is another illustration of the device of FIG. 1, particularlyidentifying the various electrodes of the set of exemplary leads; and

FIG. 10 is a functional block diagram of the device of FIG. 9, whereinthe device is a pacer/ICD, illustrating basic circuit elements thatprovide cardioversion, defibrillation and/or pacing stimulation in thefour chambers of the heart and particularly illustrating components forequipped to perform the various LV/SVT discrimination techniques ofFIGS. 2-8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description includes the best mode presently contemplatedfor practicing the invention. This description is not to be taken in alimiting sense but is made merely to describe general principles of theinvention. The scope of the invention should be ascertained withreference to the issued claims. In the description of the invention thatfollows, like numerals or reference designators will be used to refer tolike parts or elements throughout.

Overview of Implantable Medical System

FIG. 1 illustrates an implantable medical system 8 having a pacer/ICD orCRT-D 10 equipped with an event timing-based VT/SVT discriminationsystem for distinguishing VT from SVT within the patient in which thesystem is implanted. In the following examples, a pacer/ICD isdescribed. Other implantable cardiac rhythm management devices caninstead be used, such as CRT-D devices. In these examples,discrimination is achieved based on timing differences (if any) betweenLV and RV QRS complexes, along with, in at least some cases,morphological analysis of LV and RV QRS waveforms. The LV and RV QRScomplexes are sensed via a set of pacing leads 12 implanted in thepatient. In the example of FIG. 1, two leads—LV and RV—are shown (instylized form) for sensing LV and RV IEGMs signals. A more complete setof leads is illustrated in FIGS. 3-5 and FIG. 9, described below.

Upon detection of a tachyarrhythmia characterized by a high ventricularrate, the pacer/ICD analyzes LV and RV IEGM signals to detect any eventtiming differences between RV and LV QRS complexes so as to assess theorigin of tachyarrhythmia and classify the tachyarrhythmia as VT or SVT.In some examples, morphology-base discrimination is also employed. Thiswill be described in detail below. Once a determination has been made asto whether the patient is suffering from VT or SVT, pacer/ICD 10 thendelivers appropriate therapy, such as Atrial ATP in response to SVT orcardioversion shocks in response to VT.

In some embodiments, information pertaining to the tachyarrhythmia istransmitted to an external system, such as bedside monitor 14, whichgenerates diagnostic displays alerting family members or caregivers. Thebedside monitor may be directly networked with a centralized computingsystem, such as the HouseCall™ system or the Merlin@home/Merlin.Netsystems of St. Jude Medical, for immediately notifying a physician ofthe tachyarrhythmia

Warnings pertinent to the particular tachyarrhythmia may also begenerated using the bedside monitor, a hand-held personal advisorymodule (PAM), not separately shown, or an internal warning deviceprovided within the pacer/ICD. The internal warning device (which may bepart of pacer/ICD) can be a vibrating device or a “tickle” voltagedevice that, in either case, provides perceptible stimulation to thepatient to alert the patient. The bedside monitor or PAM can provideaudible or visual alarm signals to alert the patient or caregiver, aswell as any appropriate textual or graphic displays. In addition,diagnostic information pertaining to the tachyarrhythmia may be storedwithin the pacer/ICD for subsequent transmission to an externalprogrammer (not shown in FIG. 1) for review by a clinician during afollow-up session between patient and clinician. The clinician thenprescribes any appropriate therapies, such as medications. The clinicianmay also adjust the operation of the pacer/ICD to activate, deactivateor otherwise control any therapies automatically provided by the device.

Additionally, the pacer/ICD performs a wide variety of pacing and/ordefibrillation functions, such as delivering routine pacing orgenerating and delivering shocks in response to VF. Also, in someexamples, the device is equipped to deliver CRT. Briefly, CRT seeks tonormalize asynchronous cardiac electrical activation and resultantasynchronous contractions associated with CHF by delivering synchronizedpacing stimulus to both ventricles. The stimulus is synchronized so asto improve overall cardiac function. This may have the additionalbeneficial effect of reducing the susceptibility to life-threateningtachyarrhythmias.

Thus, FIG. 1 provides an overview of an implantable medical system thatincludes an event timing-based VT/SVT discrimination system. Note thatthe particular shape, size and locations of the implanted componentsshown in FIG. 1 are merely illustrative and may not necessarilycorrespond to actual implant locations. In particular, preferred implantlocations for the leads are more precisely illustrated and describedwith reference to FIG. 9.

Overview of Event Timing-based VT/SVT Discrimination

FIG. 2 provides a broad overview of the discrimination techniqueperformed by the pacer/ICD of FIG. 1. Initially, at step 100, thepacer/ICD detects intrinsic ventricular electrical events (i.e. QRScomplexes) within the patient during a tachyarrhythmia at each ofseveral of different sites within the ventricles, such as in the LV andthe RV. At step 102, the device detects event timing differences (ifany) between the events as detected at the plurality of different sites.This may be performed, for example, by comparing the timing of the peaksof corresponding QRS events as detected at the various sites. Anysignificant timing differences (especially relative to any timingdifferences that might otherwise occur during supraventricular rhythmssuch as sinus rhythm) are indicative of the origin of thetachyarrhythmia. This is shown by way of FIGS. 3-5.

FIG. 3 illustrates a normal sinus rhythm, which represents one type ofsupraventricular rhythm. Sinus rhythm originates at a sinus node 104 inthe right atrium of the heart. Electrical signals are conducted via anormal atrioventricular conduction pathway 106 via an atrioventricularnode (not shown) into the left and right ventricles. As can be seen, theconduction pathway eventually splits, with some of the signalstriggering depolarization of RV myocardial tissue at a location 108 nearthe tip electrode of the RV lead. Other signals instead propagate intothe LV, triggering depolarization of LV myocardial tissue at a location110 near the tip electrode of the LV lead. (For clarity and simplicity,the various electrodes of the implanted leads are not individuallyidentified by reference numerals in the figure. See, FIG. 9 and itsdescriptions below for further information regarding the location andfunctions of the various leads, electrodes and coils.)

Within a healthy heart, the myocardium of the LV and the RV depolarizeconcurrently during sinus rhythm such that there is no significant timedelay between the RV and LV during normal sinus rhythm. For a particularpatient, however, an intrinsic time delay between LV and RVdepolarization might occur even during sinus rhythm (or during SVT)because of conduction defects or for other reasons. Typically, anyintrinsic RV/LV depolarization delay occurring during sinus rhythm (orduring an SVT) is fairly small, at least as compared to the RV/LV delaysthat can occur during VT. As will be explained below, the intrinsicRV/LV delay (if any) occurring within the patient during sinus rhythmcan be detected by the pacer/ICD and exploited as part of the VT/SVTdiscrimination procedure.

FIG. 4 illustrates a VT with origin in the RV. The VT originates at alocation 112 in the RV. Electrical signals associated with the VT arethen conducted via an abnormal conduction pathway 114 from the RV to theLV. As can be seen, the conduction pathway first passes location 108near the RV tip electrode where RV depolarization is detected. Theconduction pathway continues into the LV where it passes location 110near the LV tip electrode where LV depolarization is detected. As can beappreciated, there can be a significant delay between RV depolarizationand LV depolarization during this type of VT, with the RV typicallydepolarizing in advance of the LV. This intrinsic RV/LV delay istypically much larger than the intrinsic RV/LV delay (if any) occurringduring sinus rhythm (or during SVT.)

FIG. 5 illustrates a VT with origin in the LV. The VT originates at alocation 120 in the LV (such as left ventricular epic.) Electricalsignals associated with the VT are then conducted via an abnormalconduction pathway 122 from the LV to the RV. In contrast to the VT ofFIG. 4, the conduction pathway of FIG. 5 first passes location 110 whereLV depolarization is detected, then continues into the RV, passinglocation 108 where RV depolarization is detected. Again, there can be asignificant delay between LV depolarization and RV depolarization duringthis type of VT, with the LV typically depolarizing in advance of theRV. This intrinsic RV/LV delay is again typically much larger than theintrinsic RV/LV delay (if any) occurring during sinus rhythm or duringSVT.

Hence, as these figures illustrate, the magnitude of the intrinsic RV/LVdepolarization delay within a patient can differ significantly betweensinus rhythms and VT. This is exploited to distinguish VT from SVT(which, like sinus rhythm, is of supraventricular origin). Typically,the delay is greater during VT than SVT (the latter of which might notexhibit any significant delay, depending upon the heart of theparticular patient.) Also, note that the sign of the RV to LVdepolarization delay can become reversed during VT as compared to sinusrhythm, depending upon the point of origin of the VT. For example, in apatient where the RV depolarizes prior to the LV during sinus rhythm,the order might be reversed during a VT originating in the LV. As such,a sign reversal in the intrinsic RV/LV delay can be indicative of a VT(at least in cases where the RV/LV delay is of sufficient magnitude forany sign reversal to be meaningful.)

Returning to FIG. 2, at step 124, the pacer/ICD compares the eventtiming differences detected at step 102 with predeterminedsupraventricular event timing differences for the patient, such as eventtiming differences detected during sinus rhythm or extrapolated fromsinus rhythm values (using techniques to be described below). In oneexample, the pacer/ICD retrieves a pre-stored supraventricular RV/LVtime delay from memory that had been determined previously for thepatient, perhaps during a post-implant follow up session between patientand clinician. That is, the device retrieves a supraventricular RV/LVdelay value representative of the type of delay occurring during asupraventricular rhythm, such as the sinus rhythm illustrated in FIG. 3.As already noted, such delays (if present) are typically relativelysmall. Additionally, or alternatively, the device can retrieveinformation representative of the sign of the supraventricular RV/LVdelay value for use in detecting any sign reversal.

At step 126, the pacer/ICD then distinguishes VT from SVT based on thecomparison of the timing differences detected during the tachyarrhythmiaand the predetermined supraventricular event timing differences for thepatient (at least in circumstances where the event timing differencesare sufficient to allow such a determination to be made.) Exemplarytechniques will be described in detail below that examine both themagnitude and the sign of any timing differences. Additionally, as willbe further explained, waveform morphology can be exploited to providefurther discrimination specificity. In addition to VT/SVTdiscrimination, the pacer/ICD, at step 126, can detect PVCs thatoriginate in the ventricles (i.e. the device can distinguish PVCs thatoriginate in the ventricles from PVCs of supraventricular origin basedon event timing differences.)

At step 128, appropriate therapy is then delivered, depending upon thecapabilities of the device and device preprogramming. In response to VT,Ventricular ATP or cardioversion might be delivered. ATP is discussedin, e.g., in U.S. Pat. Nos. 6,907,286; 7,191,002; and 7,295,873. Inresponse to SVT, atrial ATP or cardioversion might be performed (i.e.one or more shocks are delivered to the atria.) See, also, therapeutictechniques described in U.S. Pat. No. 7,245,967 that can be applied tosupraventricular arrhythmias, depending upon the capabilities of thedevice. Note also that, if the ventricular rate exceeds a thresholdindicative of VF, one or more defibrillation shocks will typically bedelivered instead. (In such cases, the discrimination procedure of FIG.1 need not be employed first. That is, upon detection of a ventricularrate indicative of VF, defibrillation shocks are promptly delivered, asVF is life threatening.)

Additionally, or alternatively, warning signals are generated (asmentioned above) and/or diagnostics data is recorded. The diagnosticscan include data pertaining to the timing delays detected within thepatient as well as the determination made by the device as to whetherthose delays are indicative of VT or SVT.

These are just some examples of operations that can be performed by theimplantable device in response to the detection and discrimination ofVT, SVT or other tachyarrhythmias. Other responses might be appropriate,as well, depending upon the needs of the patient and the capabilities ofthe implanted device.

VT/SVT Discrimination Examples

FIG. 6 illustrates a first exemplary implementation of thediscrimination technique of FIG. 2 wherein sinus rhythm timing delaysare exploited to determine supraventricular delay values withoutventricular rate adjustment. Initially, at step 200, the pacer/ICDdetects VT/SVT based on the current ventricular rate as determined,e.g., using a ventricular-IEGM signal. In one particular example, therate is continuously detected and compared against a VT/SVT threshold(set, e.g., to 150 beats per minute (bpm)) and a higher VF threshold(set, e.g., to 200 bpm). If the rate exceeds the higher VF threshold,then VF is thereby detected and defibrillation shocks are delivered. Ifthe rate only exceeds the lower VT threshold then VT/SVT is detected.Assuming VT/SVT is detected, then at steps 202 and 204, QRS events areseparately detected in the RV and the LV. For example, if theimplantable device is equipped with bipolar leads, then an RV QRS may bedetected within an RV-IEGM sensed in a bipolar sensing mode using tipand ring RV electrodes. Likewise, an LV QRS may be detected within anLV-IEGM sensed in a bipolar sensing mode using tip and ring LVelectrodes. (It should be understood that LV and RV QRS complexes aretypically detected by the device during normal device operations. Thatis, the device does not detect these events only during SVT/VT.)

At step 206, the pacer/ICD detects timing differences (if any) betweeneach RV QRS and its corresponding LV QRS and calculates an averagedifference (T_(RV-LV)). For example, the peak of the RV QRS may bedesignated as time t=0, with the delay then measured to the peak of theLV QRS. (Note that this Time Delay Will be Negative if the LVDepolarizes Before the RV.) At least several ventricular beats areexamined to detect the delays such that the delay values can be averagedtogether to yield the value for T_(RV-LV). In some examples, a runningaverage may be used.

At step 208, the pacer/ICD inputs an average timing difference(T_(RV-LV/SV)) between LV and RV QRS events that had been previouslydetected within the patient during sinus rhythm. Depending upon theparticular implementation, the value for T_(RV-LV/SV) may be determinedwhile the patient is in a sinus rhythm under clinician supervisionduring a follow-up session after device implant and then programmed intothe pacer/ICD. In other implementations, however, the pacer/ICDperiodically determines or updates T_(RV-LV/SV) whenever the patient isknown to be in sinus rhythm, so as to automatically update the value.

At step 210, the pacer/ICD compares T_(RV-LV) against T_(RV-LV/SV) todetermine a difference (T_(DIFF)) where:T_(DIFF)=|T_(RV-LV)−T_(RV-LV/SV)|. That is, T_(DIFF) represents themagnitude of the difference between the average RV-LV intrinsicdepolarization delay during the current episode of VT/SVT and theaverage RV-LV intrinsic depolarization delay during sinus rhythm for thepatient. The value of T_(DIFF) will be at or near zero if the episode ofVT/SVT does not significantly change the intrinsic RV/LV delay for thepatient (as is typically the case during SVT). Conversely, the value ofT_(DIFF) can be relatively large if the episode of VT/SVT significantlychanges the intrinsic RV/LV delay (as is typically the case during VT).

At step 212, the pacer/ICD then compares T_(DIFF) against a maxthreshold (T_(DIFF) _(—) _(MAX)) set, for example, to two times thestandard deviation of T_(RV-LV/SV). In one particular example, apredetermined value for T_(DIFF) _(—) _(MAX) is input at step 208 alongwith T_(RV-LV/SV). In other examples, T_(DIFF) _(—) _(MAX) is calculatedby the device based on input data. If T_(DIFF) exceeds this threshold(T_(DIFF)>T_(DIFF) _(—) _(MAX)), as determined at step 218, then thetachyarrhythmia is deemed to be VT. For further specificity, thepacer/ICD, at step 216, compares the signs of T_(RV-LV)−T_(RV-LV/SV) todetermine if there has been a reversal in sign. That is, the pacer/ICDdetermines whether sign(T_(RV-LV)) is equal sign(T_(RV-LV/SV)). If thesigns are not the same, then the tachyarrhythmia is VT (with the originof the VT causing the sign reversal), as indicated at step 218. Forexample, the VT might cause the LV to depolarize prior the RV; whereasthe opposite is true during sinus rhythm. The reasons for such a signreversal were discussed above in connection with FIG. 5. If the signsare the same, then the tachyarrhythmia is also a VT, but one where theorigin of the VT causes significantly different depolarization “arrival”times, as indicated at step 220. For example, the VT might arise from apoint of origin in the ventricles such that depolarization of the LV ismerely delayed relative to the RV (without a change in the order ofdepolarization.) Following either step 218 or step 220, VT therapy isdelivered and warnings/diagnostics may be generated, as alreadydiscussed.

Note that, if at step 214, T_(DIFF) does not exceed the threshold (i.e.T_(DIFF)≦T_(DIFF) _(—) _(MAX)), then the source of the tachyarrhythmiais not yet determined (i.e. the discrimination is inconclusive), asindicated at step 222. (In this case, the difference between T_(RV-LV)and T_(RV-LV/SV) is not large enough to warrant VT/SVT discrimination.That is, “noise” in the T_(RV-LV) and T_(RV-LV/SV) data may exceed anacceptable amount required to reliably distinguish VT from SVT.)Processing returns to step 200 to detect and process additional data. Insome cases, the additional data will enable the device to distinguish VTfrom SVT. If not, then additional or alternative discriminationprocedures can be employed, depending upon the capabilities of theparticular device, such as morphology-based techniques. These arediscussed in further detail below. Note also that the two times standarddeviation threshold for T_(RV) _(—) _(LV/SV) used at step 212 is merelyexemplary. Otherwise routine experimentation may be performed in advanceto determine alternative and/or optimal values for T_(DIFF) _(—) _(MAX).Such values can then be programmed into the pacer/ICD. To summarize, inone example, T_(DIFF) _(—) _(MAX) is determined as follows: measure timedifferences multiple times during sinus rhythm and then average thesinus time differences to yield T_(RV) _(—) _(LV/SV). T_(DIFF) _(—)_(MAX) can then be defined as two times the standard deviation of thesinus time difference measurements (T_(RV) _(—) _(LV/SV).)

Turning now to FIG. 7, an alternative implementation is illustrated thattakes into account the current ventricular rate when assessing thedifference between T_(RV-LV) and T_(RV-LV/SV). Many of the steps are thesame or similar to those of FIG. 6 and so only pertinent differenceswill be described in detail. At step 300, the pacer/ICD detects VT/SVTbased on the current ventricular rate and continues to track theventricular rate during the arrhythmia. Assuming VT/SVT is detected,then at steps 302 and 304, QRS events are separately detected in the RVand the LV. At step 306, the pacer/ICD then detects timing differencesbetween RV and LV QRS complexes and calculates an average difference(T_(RV-LV)).

At step 308, the pacer/ICD inputs an average supraventricular timingdifference (T_(RV-LV/SV)(rate)) between LV and RV QRS eventspre-determined for the patient for the current ventricular rate. Thisvalue may be extrapolated from sinus rhythm values. More specifically,rather than using a sinus rhythm RV-LV delay value (as in the precedingexample) for use as the supraventricular RV-LV timing delay, theembodiment of FIG. 7 instead uses sinus rhythm delay values measured atdifferent ventricular rates to estimate a corresponding RV-LV delay forthe patient at VT/SVT rates. In one particular example, the pacer/ICDobtains and stores a histogram relating RV-LV intrinsic delays toventricular rates for various sinus rhythm rates. For example, thehistogram might specify a different value for T_(RV-LV/SV) for 60-80bpm, 80-100 bpm, 100-120 bpm, 120-140 bpm, up to the VT/SVT thresholdrate. Based on these values, the pacer/ICD (or an external programmerused to program the device) extrapolates to estimate values for rates inthe VT/SVT zone, such as rates in the range of 140-160 bpm, 160-180 bpm,up to the VF threshold rate. Otherwise conventional numericalextrapolation techniques may be used to estimate these VT/SVT zonevalues from the lower sinus rhythm values.

Depending upon the particular implementation, the values forT_(RV-LV/SV)(rate) detected at sinus rhythm heart rates may bedetermined under clinician supervision during a follow-up session afterdevice implant and then programmed into the pacer/ICD. For example, thepatient may be directed to exercise so as to increase the ratethroughout a range of rates from 60 to 140 bpm so as to obtainT_(RV-LV/SV)(rate) values for various sinus rhythm rates for storage ina histogram. The external programmer then analyzes the values of thehistogram to extrapolate timing values at the higher rates in the VT/SVTzone. In some implementations, the pacer/ICD periodically determines orupdates T_(RV-LV/SV)(rate) values at sinus rhythm rates whenever thepatient is in sinus rhythm within a particular heart rate range. Thedevice then performs the analysis to extrapolate the sinus rhythm timingdelay values to yield estimated timing delays for use at the higherrates of the VT/SVT zone. Note that the number of bins in the histogramand the ranges of heart rates corresponding to each bin may beprogrammable values.

At step 310, the pacer/ICD compares T_(RV-LV) against the T_(RV-LV/SV)value for the current ventricular rate (i.e. T_(RV-LV/SV)(rate)) todetermine a difference (T_(DIFF)(rate)) where:T_(DIFF)(rate)|T_(RV-LV)−T_(RV-LV/SV)(rate)|. That is, T_(DIFF)(rate)represents the magnitude of the difference between the average RV-LVintrinsic depolarization delay during the current episode of VT/SVT andthe expected supraventricular RV-LV intrinsic depolarization delaydetermined for the patient at the current rate based on theaforementioned extrapolation. At step 312, the pacer/ICD then comparesT_(DIFF)(rate) against a max threshold (T_(DIFF) _(—) _(MAX)(rate)) set,for example, to two times the standard deviation of T_(RV-LV/SV)(rate).This standard deviation is preferably derived from the standarddeviation of multiple measurements of the supraventricular LV-RV timedifference. As such, T_(RV-LV/SV) can be interpreted as the average ofmultiple measurements of the supraventricular LV-RV time difference andT_(DIFF) _(—) _(MAX)(rate) can be set to twice the standard deviation ofthese values. If T_(DIFF) _(—) _(MAX)(rate) exceeds the threshold, asdetermined at step 318, then the tachyarrhythmia is deemed to be VT.

For further specificity, the pacer/ICD, at step 316, compares the signsof T_(RV-LV)−T_(RV-LV/SV)(rate) to determine if there has been signreversal. If the signs are not the same, then the tachyarrhythmia is VTwith the origin of the VT causing the sign reversal, as indicated atstep 318. If the signs are the same, then the tachyarrhythmia is also aVT, but one where the origin of the VT causes significantly differentdepolarization arrival times, as indicated at step 320. Following eitherstep 318 or step 320, VT therapy is delivered and warnings/diagnosticsmay be generated, as already discussed.

If at step 314, T_(DIFF)(rate) does not exceed the threshold (i.e.T_(DIFF)(rate)≦T_(DIFF) _(—) _(MAX)(rate)), then the source of thetachyarrhythmia is not yet determined (i.e. the discrimination isinconclusive), as indicated at step 322, and processing returns to step300 to detect additional data. As noted, in some cases, additional RV/LVtiming data will enable the device to distinguish VT from SVT. If not,then additional or alternative discrimination procedures can beemployed, depending upon the capabilities of the particular device, suchas morphology-based techniques.

In FIG. 8, another alternative implementation is illustrated that takesinto account the current ventricular rate when assessing the differencebetween T_(RV-LV) and T_(RV-LV/SV). In this embodiment, waveformmorphology is also examined. Many of the steps are the same or similarto those of FIG. 7 and so only pertinent differences will be describedin detail. At step 400, the pacer/ICD detects VT/SVT based on thecurrent ventricular rate and tracks the ventricular rate. At steps 402and 404, QRS events are separately detected in the RV and the LV. Atstep 406, the pacer/ICD detects timing differences between RV and LV QRScomplexes and calculates the average difference (T_(RV-LV)). Thepacer/ICD also records values representative of the shapes of the QRSwaveforms (QRS_(MORPH)). That is, the device records the time-varyingshape of the QRS or the device records some value or valuesrepresentative of that shape, such as slop, half-height width, peak,width, zero-crossing points of the QRS complex, etc. Depending upon theimplementation, QRS_(MORPH) may be based either on the LV QRS, the RVQRS or on some combination of the two.

At step 408, the pacer/ICD inputs T_(RV-LV/SV)(rate). As in thepreceding example, this value may be extrapolated from sinus rhythmvalues. At step 408, the pacer/ICD also inputs VT and SVT QRS waveformtemplates (QRS_(MORPH/VT) and QRS_(MORPH/VT)) for the patient.QRS_(MORPH/VT) represents the typical shape of the QRS within thepatient during VT. QRS_(MORPH/VT) represents the typical shape of theQRS within the patient during SVT. In one example, these waveformtemplates may be determined based on QRS waveforms detected within thepatient during previous episodes of VT and SVT within the patient. Forexample, a clinician reviews recorded IEGM data for the patient toidentify and distinguish prior episodes of VT and SVT within thepatient. Based on this determination, an external programmer thengenerates QRS waveform templates for VT and SVT for programming into thepacer/ICD. Depending upon the implementation, QRS_(MORPH/VT) andQRS_(MORPH/VT) may be based either on the LV QRS, the RV QRS or on somecombination of the two. The waveform templates may specify thetime-varying shape of the QRS or may specify some value representativeof that shape, such as the aforementioned values. In any case, duringstep 408, the pacer/ICD retrieves the previously-stored waveformtemplates from memory.

At step 410, the pacer/ICD compares T_(RV-LV) against theT_(RV-LV/SV)(rate)) to determine T_(DIFF)(rate). At step 412, thepacer/ICD then compares T_(DIFF)(rate) against T_(DIFF) _(—)_(MAX)(rate). If T_(DIFF) _(—) _(MAX)(rate) exceeds the threshold, asdetermined at step 418, then (as with the preceding example) thetachyarrhythmia is deemed to be VT. For further specificity, thepacer/ICD, at step 416, compares the signs of T_(RV-LV) to the sign ofT_(RV-LV/SV)(rate) to identify any sign reversal. If the signs are notthe same, then the tachyarrhythmia is VT with the origin of the VTcausing the sign reversal, as indicated at step 418. If the signs arethe same, then the tachyarrhythmia is also a VT, but one where theorigin of the VT causes significantly different depolarization arrivaltimes, as indicated at step 420.

If, at step 414, T_(DIFF)(rate) does not exceed the threshold T_(DIFF)_(—) _(MAX)(rate), then, at step 421, the pacer/ICD compares QRS_(MORPH)against one or both of QRS_(MORPH/SVT) and QRS_(MORPH/VT). If at step422, QRS_(MORPH) is found to be consistent with QRS_(MORPH/SVT), thenthe arrhythmia is deemed to be VT, as indicated at step 424. If at step426, QRS_(MORPH) is instead found to be consistent with QRS_(MORPH/SVT),then the arrhythmia is deemed to be SVT, as indicated at step 428.Otherwise conventional waveform comparison techniques may be employed tocompare the various waveforms to determine if the waveforms areconsistent with one another. In one example, the waveforms areconsidered to be consistent with one another is there is a substantialdegree of similarity between the shape of the waveforms as assessed bysome suitable numerical comparison parameter.

If QRS_(MORPH) is not found to be consistent with either QRS_(MORPH/VT)or QRS_(MORPH/SVT), the discrimination is deemed inconclusive, step 430.Although not shown in the figure, from step 430, processing can returnto step 400 to detect additional data. Additional RV/LV timing datacombined with additional morphological waveform data might enable thedevice to distinguish VT from SVT. If not, then additional oralternative discrimination procedures can be employed, depending uponthe capabilities of the particular device, such as alternativemorphology-based discrimination techniques. See, for example, thevarious patents cited above.

Following step 418, step 420, step 424 or step 428, suitable therapy isdelivered based on the type of arrhythmia and/or warnings/diagnosticsare generated, as already discussed.

What have been described are various exemplary techniques fordiscriminating VT and SVT using both RV and LV IEGM signals. To providefurther specificity, additional IEGMs can be exploited, such as IEGMssensed using one or more shocking coils. Sensing leads placed on or nearthe His bundle are also particularly useful for differentiating VT andSVT. Sensing sites in the atria can also be useful. Also, for multi-poleleads, various different electrode pair combinations can be exploited tosense additional IEGMs. Still further, it should be understood that thediscrimination techniques do not require both LV and RV IEGMs. In someexamples, particularly if a given LV lead or RV lead includes multipleelectrodes for multi-site sensing, the discrimination techniques mayexploit two or more IEGMs sensed in the same ventricular chamber, suchas two or more LV IEGMs, or two or more RV IEGMs. In general, anycombination near field or far field cardiac signals can be used so longas they provide a sufficient basis for distinguishing VT from SVT usingthe techniques described herein.

Note also that techniques have been described with respect to exampleswherein the implantable system performs most or all of the operations.However, principles of the invention are applicable to other systems.For example, the discrimination technique may instead be performed by anexternal device (such as a bedside monitor) based on IEGM signalsreceived from the implanted device. Exploitation of the invention withinan implanted device is preferred as it allows the device itself todetect and discriminate tachyarrhythmias so as to deliver therapypromptly but implementations exploiting external devices can be usefulas well.

For the sake of completeness, an exemplary pacer/ICD will now bedescribed, which includes components for performing the functions andsteps already described. As already noted, other implantable medicaldevices can instead be used, such as CRT-D devices. Note that, in apatient implanted with a CRT-D device, the RV lead is commonly used forpacing and sensing while the LV lead is mostly used for pacing only.However, intrinsic rhythms are presented at both leads, andstate-of-the-art CRT-D systems are capable to collect sensinginformation from the left ventricle. The characteristics and the timesequence of the sensed event collections of the two leads are differentfor supraventricular- and ventricular-originated arrhythmia, as alreadydiscussed.

Exemplary Pacer/ICD

With reference to FIGS. 9 and 10, an exemplary pacer/ICD will now bedescribed. FIG. 9 provides a simplified block diagram of the pacer/ICD,which is a dual-chamber stimulation device capable of treating both fastand slow arrhythmias with stimulation therapy, including cardioversion,defibrillation, and pacing stimulation. To provide atrial chamber pacingstimulation and sensing, pacer/ICD 10 is shown in electricalcommunication with a heart 512 by way of a right atrial lead 520 havingan atrial tip electrode 522 and an atrial ring electrode 523 implantedin the atrial appendage. Pacer/ICD 10 is also in electricalcommunication with the heart by way of a right ventricular lead 530having, in this embodiment, a ventricular tip electrode 532, a rightventricular ring electrode 534, a right ventricular (RV) coil electrode536, and a superior vena cava (SVC) coil electrode 538. Typically, theright ventricular lead 530 is transvenously inserted into the heart soas to place the RV coil electrode 536 in the right ventricular apex, andthe SVC coil electrode 538 in the superior vena cava. Accordingly, theright ventricular lead is capable of receiving cardiac signals, anddelivering stimulation in the form of pacing and shock therapy to theright ventricle.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, pacer/ICD 10 is coupled to a LV/CS lead 524designed for placement in the “CS region” via the CS os for positioninga distal electrode adjacent to the left ventricle and/or additionalelectrode(s) adjacent to the left atrium. As used herein, the phrase “CSregion” refers to the venous vasculature of the left ventricle,including any portion of the CS, great cardiac vein, left marginal vein,left posterior ventricular vein, middle cardiac vein, and/or smallcardiac vein or any other cardiac vein accessible by the CS.Accordingly, an exemplary LV/CS lead 524 is designed to receive atrialand ventricular cardiac signals and to deliver left ventricular pacingtherapy using at least a left ventricular tip electrode 526, a leftventricular ring electrode 525, left atrial pacing therapy using atleast a left atrial ring electrode 527, and shocking therapy using atleast a left atrial coil electrode 528. With this configuration,biventricular pacing can be performed. Although only three leads areshown in FIG. 5, it should also be understood that additionalstimulation leads (with one or more pacing, sensing and/or shockingelectrodes) might be used in order to efficiently and effectivelyprovide pacing stimulation to the left side of the heart or atrialcardioversion and/or defibrillation.

A simplified block diagram of selected internal components of pacer/ICD10 is shown in FIG. 10. While a particular pacer/ICD is shown, this isfor illustration purposes only, and one of skill in the art couldreadily duplicate, eliminate or disable the appropriate circuitry in anydesired combination to provide a device capable of treating theappropriate chamber(s) with cardioversion, defibrillation and pacingstimulation as well as providing for the aforementioned apnea detectionand therapy.

The housing 540 for pacer/ICD 10, shown schematically in FIG. 10, isoften referred to as the “can”, “case” or “case electrode” and may beprogrammably selected to act as the return electrode for all “unipolar”modes. The housing 540 may further be used as a return electrode aloneor in combination with one or more of the coil electrodes, 528, 536 and538, for shocking purposes. The housing 540 further includes a connector(not shown) having a plurality of terminals, 542, 543, 544, 545, 546,548, 552, 554, 556 and 558 (shown schematically and, for convenience,the names of the electrodes to which they are connected are shown nextto the terminals). As such, to achieve right atrial sensing and pacing,the connector includes at least a right atrial tip terminal (A_(R) TIP)542 adapted for connection to the atrial tip electrode 522 and a rightatrial ring (A_(R) RING) electrode 543 adapted for connection to rightatrial ring electrode 523. To achieve left chamber sensing, pacing andshocking, the connector includes at least a left ventricular tipterminal (V_(L) TIP) 544, a left ventricular ring terminal (V_(L) RING)545, a left atrial ring terminal (A_(L) RING) 546, and a left atrialshocking terminal (A_(L) COIL) 548, which are adapted for connection tothe left ventricular ring electrode 526, the left atrial ring electrode527, and the left atrial coil electrode 528, respectively. To supportright chamber sensing, pacing and shocking, the connector furtherincludes a right ventricular tip terminal (V_(R) TIP) 552, a rightventricular ring terminal (V_(R) RING) 554, a right ventricular shockingterminal (V_(R) COIL) 556, and an SVC shocking terminal (SVC COIL) 558,which are adapted for connection to the right ventricular tip electrode532, right ventricular ring electrode 534, the V_(R) coil electrode 536,and the SVC coil electrode 538, respectively.

At the core of pacer/ICD 10 is a programmable microcontroller 560, whichcontrols the various modes of stimulation therapy. As is well known inthe art, the microcontroller 560 (also referred to herein as a controlunit) typically includes a microprocessor, or equivalent controlcircuitry, designed specifically for controlling the delivery ofstimulation therapy and may further include RAM or ROM memory, logic andtiming circuitry, state machine circuitry, and I/O circuitry. Typically,the microcontroller 560 includes the ability to process or monitor inputsignals (data) as controlled by a program code stored in a designatedblock of memory. The details of the design and operation of themicrocontroller 560 are not critical to the invention. Rather, anysuitable microcontroller 560 may be used that carries out the functionsdescribed herein. The use of microprocessor-based control circuits forperforming timing and data analysis functions are well known in the art.

As shown in FIG. 10, an atrial pulse generator 570 and a ventricularpulse generator 572 generate pacing stimulation pulses for delivery bythe right atrial lead 520, the right ventricular lead 530, and/or theLV/CS lead 524 via an electrode configuration switch 574. It isunderstood that in order to provide stimulation therapy in each of thefour chambers of the heart, the atrial and ventricular pulse generators,570 and 572, may include dedicated, independent pulse generators,multiplexed pulse generators or shared pulse generators. The pulsegenerators, 570 and 572, are controlled by the microcontroller 560 viaappropriate control signals, 576 and 578, respectively, to trigger orinhibit the stimulation pulses. The microcontroller 560 further includestiming control circuitry (not separately shown) used to control thetiming of such stimulation pulses (e.g., pacing rate, atrioventricular(A-V) delay, atrial interconduction (inter-atrial or A-A) delay, orventricular interconduction (V-V) delay, etc.) as well as to keep trackof the timing of refractory periods, blanking intervals, noise detectionwindows, evoked response windows, alert intervals, marker channeltiming, etc., which is well known in the art. Switch 574 includes aplurality of switches for connecting the desired electrodes to theappropriate I/O circuits, thereby providing complete electrodeprogrammability. Accordingly, the switch 574, in response to a controlsignal 580 from the microcontroller 560, determines the polarity of thestimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) byselectively closing the appropriate combination of switches (not shown)as is known in the art.

Atrial sensing circuits 582 and ventricular sensing circuits 584 mayalso be selectively coupled to the right atrial lead 520, LV/CS lead524, and the right ventricular lead 530, through the switch 574 fordetecting the presence of cardiac activity in each of the four chambersof the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR.SENSE) sensing circuits, 582 and 584, may include dedicated senseamplifiers, multiplexed amplifiers or shared amplifiers. The switch 574determines the “sensing polarity” of the cardiac signal by selectivelyclosing the appropriate switches, as is also known in the art. In thisway, the clinician may program the sensing polarity independent of thestimulation polarity. Each sensing circuit, 582 and 584, preferablyemploys one or more low power, precision amplifiers with programmablegain and/or automatic gain control and/or automatic sensitivity control,bandpass filtering, and a threshold detection circuit, as known in theart, to selectively sense the cardiac signal of interest. The outputs ofthe atrial and ventricular sensing circuits, 582 and 584, are connectedto the microcontroller 560 which, in turn, are able to trigger orinhibit the atrial and ventricular pulse generators, 570 and 572,respectively, in a demand fashion in response to the absence or presenceof cardiac activity in the appropriate chambers of the heart.

For arrhythmia detection, pacer/ICD 10 utilizes the atrial andventricular sensing circuits, 582 and 584, to sense cardiac signals todetermine whether a rhythm is physiologic or pathologic. As used herein“sensing” is reserved for the noting of an electrical signal, and“detection” is the processing of these sensed signals and noting thepresence of an arrhythmia. The timing intervals between sensed events(e.g., AS, VS, and depolarization signals associated with fibrillationwhich are sometimes referred to as “F-waves” or “Fib-waves”) are thenclassified by the microcontroller 560 by comparing them to a predefinedrate zone limit (i.e., bradycardia, normal, atrial tachycardia, atrialfibrillation, low rate ventricular tachycardia, high rate ventriculartachycardia, and fibrillation rate zones) and various othercharacteristics (e.g., sudden onset, stability, physiologic sensors, andmorphology, etc.) in order to determine the type of remedial therapythat is needed (e.g., bradycardia pacing, ATP, cardioversion shocks ordefibrillation shocks).

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 590. The data acquisition system 590 isconfigured to acquire intracardiac electrogram signals, convert the rawanalog data into a digital signal, and store the digital signals forlater processing and/or telemetric transmission to an external device602. The data acquisition system 590 is coupled to the right atrial lead520, the LV/CS lead 524, and the right ventricular lead 530 through theswitch 574 to sample cardiac signals across any pair of desiredelectrodes. The microcontroller 560 is further coupled to a memory 594by a suitable data/address bus 596, wherein the programmable operatingparameters used by the microcontroller 560 are stored and modified, asrequired, in order to customize the operation of pacer/ICD 10 to suitthe needs of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude or magnitude, pulse duration, electrodepolarity, rate, sensitivity, automatic features, arrhythmia detectioncriteria, and the amplitude, waveshape and vector of each shocking pulseto be delivered to the patient's heart within each respective tier oftherapy. Other pacing parameters include base rate, rest rate andcircadian base rate.

Advantageously, the operating parameters of the implantable pacer/ICD 10may be non-invasively programmed into the memory 594 through a telemetrycircuit 600 in telemetric communication with the external device 602,such as a programmer, transtelephonic transceiver or a diagnostic systemanalyzer, or with a beside monitor 14. The telemetry circuit 600 isactivated by the microcontroller by a control signal 606. The telemetrycircuit 600 advantageously allows intracardiac electrograms and statusinformation relating to the operation of pacer/ICD 10 (as contained inthe microcontroller 560 or memory 594) to be sent to the external device602 through an established communication link 604. Pacer/ICD 10 furtherincludes an accelerometer or other physiologic sensor 608, commonlyreferred to as a “rate-responsive” sensor because it is typically usedto adjust pacing stimulation rate according to the exercise state of thepatient. However, the physiological sensor 608 may further be used todetect changes in cardiac output, changes in the physiological conditionof the heart, or diurnal changes in activity (e.g., detecting sleep andwake states) and to detect arousal from sleep. Accordingly, themicrocontroller 560 responds by adjusting the various pacing parameters(such as rate, A-V delay, V-V delay, etc.) at which the atrial andventricular pulse generators, 570 and 572, generate stimulation pulses.While shown as being included within pacer/ICD 10, it is to beunderstood that the physiologic sensor 608 may also be external topacer/ICD 10, yet still be implanted within or carried by the patient. Acommon type of rate responsive sensor is an activity sensorincorporating an accelerometer or a piezoelectric crystal, which ismounted within the housing 540 of pacer/ICD 10. Other types ofphysiologic sensors are also known, for example, sensors that sense theoxygen content of blood, respiration rate and/or minute ventilation, pHof blood, ventricular gradient, PPG etc. Multiple sensors may beprovided.

The pacer/ICD additionally includes a battery 610, which providesoperating power to all of the circuits shown in FIG. 10. The battery 610may vary depending on the capabilities of pacer/ICD 10. If the systemonly provides low voltage therapy, a lithium iodine or lithium copperfluoride cell may be utilized. For pacer/ICD 10, which employs shockingtherapy, the battery 610 must be capable of operating at low currentdrains for long periods, and then be capable of providing high-currentpulses (for capacitor charging) when the patient requires a shock pulse.The battery 610 must also have a predictable discharge characteristic sothat elective replacement time can be detected. Accordingly, pacer/ICD10 is preferably capable of high voltage therapy and appropriatebatteries.

As further shown in FIG. 10, pacer/ICD 10 is shown as having animpedance measuring circuit 612 which is enabled by the microcontroller560 via a control signal 614. Thoracic impedance may be detected for usein tracking thoracic respiratory oscillations; lead impedancesurveillance during the acute and chronic phases for proper leadpositioning or dislodgement; detecting operable electrodes andautomatically switching to an operable pair if dislodgement occurs;measuring respiration or minute ventilation; measuring thoracicimpedance for determining shock thresholds; detecting when the devicehas been implanted; measuring respiration; and detecting the opening ofheart valves, etc. The impedance measuring circuit 612 is advantageouslycoupled to the switch 574 so that any desired electrode may be used.

In the case where pacer/ICD 10 is intended to operate as an implantablecardioverter/defibrillator (ICD) device, it detects the occurrence of anarrhythmia, and automatically applies an appropriate electrical shocktherapy to the heart aimed at terminating the detected arrhythmia. Tothis end, the microcontroller 560 further controls a shocking circuit516 by way of a control signal 618. The shocking circuit 516 generatesshocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules) orhigh energy (11 to 40 joules), as controlled by the microcontroller 560.Such shocking pulses are applied to the heart of the patient through atleast two shocking electrodes, and as shown in this embodiment, selectedfrom the left atrial coil electrode 528, the RV coil electrode 536,and/or the SVC coil electrode 538. The housing 540 may act as an activeelectrode in combination with the RV electrode 536, or as part of asplit electrical vector using the SVC coil electrode 538 or the leftatrial coil electrode 528 (i.e., using the RV electrode as a commonelectrode). Cardioversion shocks are generally considered to be of lowto moderate energy level (so as to minimize pain felt by the patient),and/or synchronized with a VF event and/or pertaining to the treatmentof tachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40joules), delivered asynchronously (since VF events may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 560 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

Insofar as tachyarrhythmia discrimination is concerned, themicrocontroller includes a rate-based VT/SVT/VF detector 601 operativeto detect a tachyarrhythmia affecting the ventricles based on theventricular rate by, e.g., using one or more rate thresholds (such as aVT/SVT threshold and a higher VF threshold.) A VT/SVT discriminationsystem 603 is operative to distinguish VT from SVT in accordance withthe techniques generally described above. The VT/SVT discriminationsystem includes an LV/RV event timing difference detector 605 operativeto detect event timing differences between ventricular events asdetected at a plurality of different sites within the ventricles via theRV and LV/CS leads. An LV/RV event timing difference comparison system619 is operative to compare the ventricular event timing differencesdetected during the tachyarrhythmia with predetermined supraventricularevent timing differences for the patient retrieved from memory 594. Anevent timing-based discrimination system 607 is operative to distinguishVT from SVT based on the comparison of the event timing differences madeby LV/RV event timing difference comparison system 619, at least incircumstances where such a discrimination can be made.

Additionally, an LV/RV event morphology detection/comparison system 609is operative to detect the morphology of the ventricular events andcompare the morphology with VT and SVT morphology templates retrievedfrom memory 594. A waveform morphology-based discrimination system 611is provided to further discriminate VT from SVT based on the waveformcomparison made by morphology detection/comparison system 609.

A therapy controller 613 is operative to control delivery of therapybased on whether the ventricular arrhythmia is SVT or VT, such as bycontrolling the delivery of ATP. A warning/diagnostics controller 615controls the generation of warning signals and diagnostic data based onthe results of the operation of the other units of the microcontroller,such as the generation of warning signals for relaying to bedsidemonitor 14 to notify the patient and/or physician of the onset, durationand type of various tachyarrhythmias. Warning signals may be deliveredto the patient via a warning device 617, which may be, e.g., avibrational warning device or a device that provide a perceptible“tickle” voltage.

Depending upon the implementation, the various components of themicrocontroller may be implemented as separate software modules or themodules may be combined to permit a single module to perform multiplefunctions. In addition, although shown as being components of themicrocontroller, some or all of these components may be implementedseparately from the microcontroller, as application specific integratedcircuits (ASICs) or the like.

As noted, at least some of the discrimination steps or functions can beperformed by an external device based on signals sent from thepacer/ICD. This is illustrated by way of VT/SVT discrimination system621 of external programmer 602. Additionally or alternatively, thebedside monitor may also be equipped with such components.

In general, while the invention has been described with reference toparticular embodiments, modifications can be made thereto withoutdeparting from the scope of the invention. Note also that the term“including” as used herein is intended to be inclusive, i.e. “includingbut not limited to.”

1. A method for use by an implantable medical device capable ofmulti-site ventricular sensing within a patient, the method comprising:detecting intrinsic ventricular electrical events within the patientduring a tachyarrhythmia at each of a plurality of different siteswithin the ventricles; detecting ventricular event timing differencesbetween the ventricular events as detected at the plurality of differentsites; comparing the ventricular event timing differences detectedduring the tachyarrhythmia with predetermined supraventricular eventtiming differences for the patient; and distinguishing a ventriculartachycardia (VT) from a supraventricular tachycardia (SVT) based on thecomparison of the ventricular event timing differences detected duringthe tachyarrhythmia with the predetermined supraventricular event timingdifferences.
 2. The method of claim 1 wherein the device is equippedwith left ventricular (LV) and right ventricular (RV) leads and whereindetecting intrinsic ventricular electrical events during thetachyarrhythmia at each of a plurality of different sites within theventricles includes separately detecting ventricular events within theRV and within the LV.
 3. The method of claim 2 wherein detectingventricular timing differences LV includes detecting RV-LV timingdifferences (T_(RV-LV)) between the ventricular events as detected inthe RV and in the LV.
 4. The method of claim 3 wherein comparing theventricular timing differences detected during the tachyarrhythmia withthe predetermined supraventricular event timing differences includes:comparing ventricular timing differences (T_(RV-LV)) detected during thetachyarrhythmia with predetermined supraventricular timing differences(T_(RV-LV/SV)) detected within the patient during a prior sinus rhythm.5. The method of claim 4 wherein distinguishing VT from SVT includes:identifying the tachyarrhythmia as VT if a magnitude of the differencebetween T_(RV-LV) and T_(RV-LV/SV) exceeds a predetermined threshold. 6.The method of claim 4 wherein distinguishing VT from SVT includes:identifying the tachyarrhythmia as VT if T_(RV-LV) and T_(RV-LV/SV) havea different sign.
 7. The method of claim 4 wherein average values forT_(RV-LV) and T_(RV-LV/SV) are employed in the comparison.
 8. The methodof claim 3 further including detecting a current ventricular rate duringthe tachyarrhythmia.
 9. The method of claim 8 wherein comparing theventricular timing differences detected during the tachyarrhythmia withthe predetermined supraventricular event timing differences includes:comparing ventricular timing differences (T_(RV-LV)) detected during thetachyarrhythmia at the current ventricular rate with predeterminedsupraventricular timing differences (T_(RV-LV/SV)(rate)) determined forthe patient for substantially the same ventricular rate.
 10. The methodof claim 9 further including the prior steps of: detecting ventriculartiming differences (T_(RV-LV/SV)(rate)) within the patient for a rangeof ventricular rates during sinus rhythm; and estimating ventriculartiming differences (T_(RV-LV/SV)(rate)) for the patient for rates withina VT/SVT zone by extrapolating from the timing differences detectedduring sinus rhythm.
 11. The method of claim 9 wherein distinguishing VTfrom SVT includes: identifying the tachyarrhythmia as VT if a magnitudeof the difference between T_(RV-LV) and T_(RV-LV/SV)(rate) exceeds apredetermined threshold.
 12. The method of claim 9 whereindistinguishing VT from SVT includes: identifying the tachyarrhythmia asVT if T_(RV-LV) and T_(RV-LV/SV)(rate) have a different sign.
 13. Themethod of claim 9 wherein average values for T_(RV-LV) andT_(RV-LV/SV)(rate) are employed in the comparison for the currentventricular rate.
 14. The method of claim 3 further including: detectingventricular event morphology (QRS_(MORPH)) during the tachyarrhythmia;and comparing ventricular event morphology (QRS_(MORPH)) detected duringthe tachyarrhythmia with predetermined ventricular event morphologytemplates.
 15. The method of claim 14 wherein comparing the ventriculartiming differences detected during the tachyarrhythmia with thepredetermined supraventricular event timing differences includes:comparing ventricular timing differences (T_(RV-LV)) detected during thetachyarrhythmia at the current ventricular rate with predeterminedsupraventricular timing differences (T_(RV-LV/SV)(rate)) determined forthe patient for substantially the same ventricular rate.
 16. The methodof claim 15 wherein distinguishing VT from SVT includes: identifying thetachyarrhythmia as VT if a magnitude of the difference between T_(RV-LV)and T_(RV-LV/SV)(rate) exceeds a predetermined threshold and thedetected ventricular events have a morphology consistent with VT. 17.The method of claim 15 wherein distinguishing VT from SVT includes:identifying the tachyarrhythmia as VT if T_(RV-LV) andT_(RV-LV/SV)(rate) differ in sign and the detected ventricular eventshave a morphology consistent with VT.
 18. The method of claim 15 whereindistinguishing VT from SVT includes: identifying the arrhythmia as SVTif a magnitude of the difference between T_(RV-LV) andT_(RV-LV/SV)(rate) does not exceed a predetermined threshold and thedetected ventricular events have a morphology consistent with SVT. 19.The method of claim 1 further including detecting premature ventricularcontractions (PVCs) that originate in the ventricles.
 20. The method ofclaim 1 wherein the tachyarrhythmia is initially detected based on aventricular rate exceeding a rate threshold.
 21. The method of claim 1further including delivering therapy in response to the tachyarrhythmia.22. A system for use by an implantable medical device capable ofmulti-site ventricular sensing within a patient, the system comprising:an intrinsic electrical event detection system operative to detectintrinsic ventricular electrical events during a tachyarrhythmia at eachof a plurality of different sites within the ventricles; a ventricularevent timing difference detection system operative to detect eventtiming differences between the ventricular events as detected at theplurality of different sites; a ventricular event timing comparisonsystem operative to compare the event timing differences detected duringthe tachyarrhythmia with predetermined supraventricular event timingdifferences for the patient; and a tachyarrhythmia discrimination systemoperative to distinguish ventricular tachycardia (VT) fromsupraventricular tachycardia (SVT) within the patient based on thecomparison of the ventricular event timing differences detected duringthe tachyarrhythmia with the predetermined supraventricular event timingdifferences.
 23. A system for use by an implantable medical devicecapable of multi-site ventricular sensing within a patient, the systemcomprising: means for detecting intrinsic ventricular electrical eventswithin the patient during a tachyarrhythmia at each of a plurality ofdifferent sites within the ventricles; means for detecting ventricularevent timing differences between the events as detected at the pluralityof different sites; means for comparing the ventricular event timingdifferences detected during the tachyarrhythmia with predeterminedsupraventricular event timing differences for the patient; and means fordistinguishing a ventricular tachycardia (VT) from a supraventriculartachycardia (SVT) based on the comparison of the ventricular eventtiming differences detected during the tachyarrhythmia with thepredetermined supraventricular event timing differences.